docs: def set_alias(index_name, delete=True):
      '''
      Properly end an indexation by creating an alias.
      Previous alias is deleted if needed.
      '''
      log.info('Creating alias "{0}" on index "{1}"'.format(
          es.index_name, index_name))
      if es.indices.exists_alias(name=es.index_name):
          alias = es.indices.get_alias(name=es.index_name)
          previous_indices = alias.keys()
          if index_name not in previous_indices:
              es.indices.put_alias(index=index_name, name=es.index_name)
          for index in previous_indices:
              if index != index_name:
                  es.indices.delete_alias(index=index, name=es.index_name)
                  if delete:
                      es.indices.delete(index=index)
      else:
          es.indices.put_alias(index=index_name, name=es.index_name)